Fatty acids with conjugated double bonds are well known naturally occurring compounds. Most fatty acids or fatty acid derivatives are single chain hydrocarbon molecules, with from 3 to up to 22 or more carbons. Many naturally occurring fatty acids are unsaturated, which means that they have at least one double bond; a fatty acid with two or more double bonds is referred to as polyunsaturated fatty acid. (The presence of a single double bond results in an enyne, two in a diene, three in a triene, four in a tetraene, five in a pentaene, six in a hexaene, seven in a heptaene, etc.) Most double bonds in polyunsaturated fatty acids are unconjugated polyenes, or methylene-interrupted polyenes, in that the double bonds are separated by a methyl group. However, in fewer cases, double bonds are conjugated, in that two double bonds are separated only by a single bond. Among naturally occurring conjugated polyenes, conjugated dienes and trienes are the most prevalent. Each conjugated double bond can exist in one of two isomeric forms: cis (referred to as c or Z), or trans (referred to as t or E).
Conjugated fatty acids have numerous commercial utilities. One is in drying oils. Drying oils are of value due to their ability to polymerize or dry after application to a surface to form tough, adherent and abrasion-resistant films. Upon exposure to oxygen, unconjugated polyenes, such as those contained in linseed oil and tung oil, oxidize and cross-link to form such films; however, conjugated polyenes cross-link more rapidly, are thus valued by the paint and varnish industries for use in drying oils.
Another utility is in the area of health and nutrition. Research has shown that conjugated polyenes may inhibit tumor growth, prevent heart disease, and reduce body fat. For example, investigations of the biological activity of conjugated fatty acids have suggested that they possess anti-arteriosclerosis effects, boost the immune system, and affect energy metabolism, promoting protein deposition while decreasing fat deposition. Yet another use is the presence of conjugated fatty acids in many insect pheromone blends.
Yet another utility is as research reagents. Long chain conjugated polyenes can be both fluorescent and photoreactive, and thus useful as probes or markers. For example, parinaric acid, a naturally occurring polyconjugated fatty acid, has been utilized as a fluorescent membrane probe to detect phase transitions in bilayers as well as interactions between lipids and proteins. Parinaric acid can be biosynthetically incorporated into phospholipids, and its environment examined thorough spectroscopic characterization. Additional information about the dynamics of membrane behavior as well as interactions between proteins and lipids can be obtained by using other conjugated double bond systems (e.g., with the chromophore in the middle of the fatty acid or near the carboxyl group (Goerger M. M. and Hudson B. S. (1988) J. Org. Chem. Vol. 53, No. 14, pp. 3148–3153). It appears that both the number and location of the conjugated double bonds within the fatty acid chain can affect the utility of the molecule as a research probe.
Although some polyconjugated fatty acids are naturally occurring (for example, several examples have been identified in marine plants), these fatty acids occur in limited quantities and in limited conformations. Thus, there is a need to develop other polyconjugated fatty acids with different conformations. There is also a need to provide other polyconjugated fatty acids in sufficient quantities to use as research tools, and potentially to use as nutritional supplements or as drugs or as platforms for developing drugs.
Although some methods exist to prepare conjugated polyenes, investigators continue to seek more efficient methods, as well as methods which can manipulate either the number and/or the location of the conjugated double bonds within a single fatty acid or fatty acid derivative. Moreover, methods are also sought which control the isomeric form of each conjugated double bond.